@techreport {TR-1991-023,
   type = {Technical Report},
   author = {Andrzej Proskurowski },
   title = {Graph Reductions, and Techniques for Finding Minimal Forbidden Minors},
   institution = {University of Oregon, Computer and Information Sciences Department},
   number = TR-1991-023,
   month = 10,
   year = 1991,
   note = {Available at \url{https://www.cs.uoregon.edu/Reports/TR-1991-023.pdf}},
}